1. Field of the Invention
The present invention relates to an airtight terminal and its fabricating method, a piezoelectric vibrator and its fabricating method, an oscillator, an electronic apparatus and a radio wave timepiece.
2. Description of the Related Art
A piezoelectric vibrator is used as a reference oscillation source of an electronic apparatus, an oscillation piece of an oscillator, a clock source of a microcomputer or the like. As a package of the piezoelectric vibrator, a ceramic package constituted by a box type shape, a cylinder package type including a lead is commonly used.
Here, a constitution of a piezoelectric vibrator of a cylinder package type of a background art will be explained.
FIGS. 21A and 21B show a background art of a piezoelectric vibrator 01 of a cylinder package type, wherein FIG. 21A is a perspective view showing a total constitution, and FIG. 21B is a partial sectional view showing a state of cutting a portion of a stem along a longitudinal direction of a lead.
The piezoelectric vibrator 01 is constituted by an airtight terminal 010, a piezoelectric vibrating piece 020, a case 030 as principal members.
Among the principal parts, the airtight terminal 010 is constituted by a stem 011 in a cylindrical shape, 2 pieces of parallel leads 012 arranged to penetrate inside of the stem 011, a filling member 013 filled at inside of the stem 011 for fixing 2 pieces of the leads 012 at inside of the stem 011.
The stem 011 is formed by, for example, 42 alloy (Fe—Ni), and a surface thereof is subjected to plating 014 having a thickness of substantially 10 μm through 15 μm. As the plating 014, Cu plating is carried out as a matrix, and a tin lead alloy plating (Sn—Pb plating) is carried out thereon as finish plating. Further, in FIG. 21B, the plating thickness of the plating 014 is exaggeratedly illustrated.
2 pieces of the leads 012 comprising solid round bars made of a metal are supported at inside of the stem 011 in a state of penetrating inside of the stem 011, that is, a state of penetrating the filling member 013 filled at inside of the stem 011 by way of the filling member 013.
In other words, 2 pieces of the leads 012 are protruded from one end face (end face of upper side shown in FIG. 21A) and protruded from other end face (end face of lower side shown in FIG. 21A) of the stem 011 by interposing the stem 011 filled with the filling member 013 at inside thereof. Generally, a portion thereof protruded from the one end face (end face of upper side shown in FIG. 21A) of the stem 011 is referred to as “inner lead 012a” and a portion thereof protruded from the other end face (end face of lower side shown in FIG. 21A) of the stem 011 is referred to as “outer lead 012b”. 
A surface of the lead 012 (including both of inner leads 012a and outer lead 012b) is subjected to plating 015 having a thickness of substantially 10 μm through 15 μm. As the plating 015, for example, Cu plating is carried out as matrix, and Sn—Pb plating is carried out thereon as finish plating.
The filling member 013 is formed by, for example, borosilicate glass, and a thermal expansion rate thereof becomes substantially equal to that of the stem 011 or the lead 012. The filling member 013 is filled in a space at inside of the stem 011 and supports the lead 012.
The piezoelectric vibrating piece 020 is constituted by forming quartz in a tuning fork type and including an exciting electrode (not illustrated) and a mount pad 021 on a surface thereof.
The mount pad 021 of the piezoelectric vibrating piece 020 and the inner lead 012a of the airtight terminal 010 are electrically and mechanically connected. The connection is carried out by locally melting the plating 015 provided at the surface of the inner lead 012a in the atmosphere and connecting the mount pad 021 and the inner lead 012a by the melted plating.
The case 030 is constituted by a shape of a bottomed cylinder opening one end face (lower end face in FIG. 21A) and closing other end face (upper end face in FIG. 21A) and constituted by subjecting a surface of nickel silver (brass Ni alloy) to Ni plating.
The case 030 is constituted by capping an opening end face side of the case 030 to an outer peripheral face of the stem 011 tightly by tight fitting to cover the inner lead 012a and the piezoelectric vibrating piece 020 to be contained to an inner space thereof. At this occasion, the plating 014 constituting a soft metal is subjected to cold pressure welding to realize airtight bonding.
Further, in FIG. 21A the case 030 is illustrated in a transparent state to facilitate understanding by optically recognizing an inner state of the case 030.
A method of automating to fabricate such a piezoelectric vibrator is disclosed (for example, JP-A-8-316761).
Meanwhile, in recent years, rapid downsizing of an electronic part is requested, and according to a fabricating method of a background art, it is very difficult to fabricate a small-sized piezoelectric vibrator with excellent yield at low cost and highly reliably.
There are two principal problems thereof. A first problem is an increase in cost of fabricating an airtight terminal by a reduction in yield in plating at a step of fabricating the airtight terminal. The second problem is a problem of a reduction in a rigidity of an outer lead of an airtight terminal.
A concise description will be given of the two problems as follows.
A significant reduction in yield in plating in accordance with downsizing an airtight terminal constituting the first problem is caused by narrowing an interval between leads and a reduction in a rigidity by reduction in a wire diameter of a lead.
A diameter of a piezoelectric vibrator of a cylinder package type (which is a maximum value of an outer shape of a case after having been sealed and is designated by notation D in FIG. 21A) is reduced from about 3 mm to 2 mm, and becomes 1.5 mm. In recent years, downsizing is further progressed for a piezoelectric vibrator used in a portable telephone and a diameter of 1.2 mm is used. The tendency is further progressed, and a dimension smaller than 1 mm has been investigated to adopt.
By such progress of downsizing, an interval of 2 pieces of leads (designated by notation d1 in FIG. 21A) constituting members of an airtight terminal becomes extremely narrow, further, also a diameter of the lead per se (designated by notation d2 in FIG. 21A) becomes slender, a rigidity thereof is reduced and the lead is liable to be bent easily.
A plating step of a background art is of a barrel plating type advantageous for mass production. A shape of vessel is constituted by a hexagonal column having, for example, a diameter of several tens cm and a length of about 40 cm through 80 cm and is made of resin of acrylic resin or the like. Electric plating is carried out by putting airtight terminals of a number of about 200 thousands through 500 thousands into the vessel and taking several hours while slowly rotating the vessel at inside of a plating tank to agitate the airtight terminals at inside thereof.
In the step, particularly in a case of a small-sized airtight terminal of D=1.2 mm or the like, the lead interval is narrow, the lead per se is liable to be bent easily and therefore, a failure of bridging plating between the leads, or a failure of entwining the outer leads is frequently brought about. Thereby, there poses a problem that yield in plating is considerably reduced, and cost of fabricating the airtight terminal is considerably increased.
The second problem is a reduction in the rigidity of the outer lead of the airtight terminal. Although a reduction in the rigidity of the outer lead has been indicated as the problem also in fabricating the airtight terminal constituting the first problem, here, the second problem is posed as a problem having other aspect which is posed in a step of integrating the piezoelectric vibrating piece. The problem is related to the inner lead in accordance with downsizing the piezoelectric vibrating piece.
When the piezoelectric vibrating piece is further downsized in the future, an area of a mount pad on a piezoelectric vibrating piece is narrowed and a gap between the piezoelectric vibrating piece and the mount pad is reduced. Therefore, it is a problem how to constitute a fine positional relationship between a front end of an inner lead of an airtight terminal bonded to the mount pad and the mount pad. At the same time, an outer lead is aligned and held mechanically in a pallet in an integrating step and therefore, the outer lead needs a rigidity so as not to be bent in the integrating step.
According to the lead of the airtight terminal of the background art, a total of the lead is constituted by a solid round bar having a uniform diameter from an easiness in fabrication. However, when a method of the background art which has been improving an accuracy of positioning the mount pad and the front end of the inner lead by making the diameter of the inner lead in accordance with a reduction in the area of the mount pad of the piezoelectric vibrating piece is assumedly followed, also the diameter of the outer lead is similarly made to be slender and the rigidity becomes deficient. For example, when the lead diameter is constituted by 50 μm in a case of the width of the mount pad of 50 μm, the lead is simply bent to be clearly deficient in the rigidity. According to the airtight terminal of the structure of the background art in which the inner lead and the outer lead are provided with the same diameter, there is a concern of being unable to deal with downsizing sufficiently.
Further, also a piezoelectric vibrator having one piece of a lead has been developed in order to ensure a rigidity of the lead (for example, JP-A-2002-43886). In this case, although the piezoelectric vibrator is formed with two of mount pads, one of the mount pads is electrically and mechanically connected to one piece of the lead and other of the mount pads is electrically and mechanically connected to a stem by way of a conductive member or the like functioning as the lead.
When the lead is constituted by one piece in this way, it is not necessary to take a lead interval into consideration and therefore, downsizing can be achieved by that amount. However, a method of fabricating the airtight terminal constituting the lead by one piece with excellent yield has not been established yet.
In view of the above-described background art, it is an object of the invention to provide an airtight terminal and a piezoelectric vibrator having a strong rigidity of a lead and eliminating a failure in plating even by a small size and a method of fabricating an airtight terminal or a piezoelectric vibrator constituting a lead penetrated at inside of a stem by one piece with excellent yield.